This C++26 change was just approved in Tokyo, in P2944R3. It adds
operator== and operator<=> overloads to std::reference_wrapper.
The operator<=> overloads in the paper cause compilation errors for any
type without <=> so they're implemented here with deduced return types
and constrained by a requires clause.
libstdc++-v3/ChangeLog:
* include/bits/refwrap.h (reference_wrapper): Add comparison
operators as proposed by P2944R3.
* include/bits/version.def (reference_wrapper): Define.
* include/bits/version.h: Regenerate.
* include/std/functional: Enable feature test macro.
* testsuite/20_util/reference_wrapper/compare.cc: New test.
0d58450659